DESCRIPTION: Viruses are intimately associated with their host's cellular machinery, so molecular interactions between viral and host cell components are important factors which determine viral host range and pathogenesis. In contrast to the situation for animal-infecting viruses, little is known about the molecular interactions which determine the host-adaptation of plant viruses. This proposal focuses on geminiviruses, which are plant-infecting viruses with small DNA genomes. Geminiviruses cause agricultural problems in tropical and subtropical regions world-wide, and in developing countries they can affect public health through their impact on the food supply. An experimental strategy for the elucidation of virus-host interactions will be developed using two geminiviruses, and the plant hosts to which they are differentially adapted. In this model system, host adaptation is determined by a combination of (i) the viral proteins which potentiate movement between host cells; and (ii) the cis-and trans-acting viral factors that are required for late gene expression (the late promoters and a transcriptional control protein). The specific aims of this project are to identify and characterize the plant proteins which interact with host-adapted geminiviral proteins and late promoters. Interaction-cloning methods will be employed to identify candidate host proteins. Characterization will involve nucleotide sequencing, determination of gene expression patterns, immunochemical localization of the protein, and biochemical confirmation of its interaction with viral factors. The role of the identified host proteins in both healthy and virus-infected plants will be evaluated. The results of these experiments will provide important new information on the molecular mechanisms which underlie the control of gene expression, and the intra- and intercellular trafficking of macromolecules in plants. The long-term objective of this research is to define the molecular interactions between geminivirus and host components in host plant species. The approaches developed during the course of this research should also be generally applicable to the analysis of host range and pathogenicity determinants in any viral system in which closely related viruses exhibit distinct host-specific phenotypes.